Workers installing sheet material such as drywall, plywood, insulation, and moisture barrier wraps use tools or improvised devices for marking or scribing straight construction lines on the material to aid in its cutting or fastening to a support structure such as a stud, rafter or joist. The construction lines must be drawn accurately to minimize waste and ensure that the material will be properly fastened, and a good deal of time is often spent in repeatedly measuring and marking. Accordingly, what is needed is an improved and cost-effective line marking apparatus for quickly and accurately producing straight construction lines.